1. Field of the Invention
This invention relates to grey-level, ultrasonic imaging and, more specifically, provides a system and method of establishing grey-level, ultrasonic images while employing conventional ultrasonic signal generating means and a bistable storage oscilloscope.
2. Description of the Prior Art
It has been known to employ ultrasonic B-scan type equipment in diagnostic medical procedures as well as in other uses. In such an arrangement, in connection with use on a human or animal patient or specimen, an ultrasonic pulse is generated by the piece of ultrasonic testing equipment. The ultrasonic wave impinges upon the patient, and a number of reflected waves are sent back into the instrument. In a conventional system, the signal is then converted into an electrical signal which is visually displayed upon a bistable storage oscilloscope. In the bistable storage oscilloscope, the amplitude of the voltage of the electrical signal, which is related to the ultrasonic reflected wave, is divided at a certain threshold level. The voltage wave portions which are under that threshold level appear on the storage oscilloscope screen as black. The voltage wave portions which are higher than the threshold level are displayed as white dots or bars. In this fashion, a picture of the portion of the patient or specimen examined is displayed in what amounts to a "go-no go" approach. This approach to the use of ultrasonics has severe limitations in that establishing the decision of threshold voltage level is somewhat arbitrary, and the use of a bistable system precludes the visualization of "fine structure" information regarding the patient or specimen. Even in situations where a more complex "decision threshold" is established, such as through use of time derivative functions of the reflected signals, the basic inability to show refined pictures of the patient or specimen remains a problem.
Efforts have been made to refine the picture presented by conventional oscilloscopes, as well as by bistable storage oscilloscopes.
U.S. Pat. No. 3,902,476 discloses pulse width modulation as applied to medical diagnostic ultrasonics. In this disclosure, the connected dot-pattern displays are purposely elongated into overlapping or connected dashes in an effort to improve visual continuity in electronic graphic displays and to improve the visually apparent frequency response in such displays. Primary emphasis is directed toward improving bistable displays in connection with cardiac echocardiography.
U.S. Pat. No. 3,881,466 discloses ultrasonic cross-sectional imaging wherein the system includes an array of transverse transducer elements which are sequentially pulsed. The rectified radio-frequency return ultrasonic echoes are converted into voltages proportional to the logarithms of the return echo amplitudes.
U.S. Pat. Nos. 3,156,110 and 3,292,018 acknowledge the weakness of bistable displays in respect of maximum possible diagnostic value in ultrasonic inspections both of living organisms and industrial flaw detection applications. These patents suggest approaches which involve the use of several ultrasonic frequencies which in turn provide return echoes differentiated by frequency to produce multicolored display patterns. Emphasis is placed upon the time-motion (TM) mode and the time exposure color photography.
U.S. Pat. No. 3,779,234 discloses the use of a sinecosine potentiometer as a means for producing B-scans. Angular information from the sine-cosine potentiometer is derived from a rotating machine as distinguished from manual motion of an ultrasonographer's hand manipulations. U.S. Pat. No. 3,690,311 discloses the use of rate derivatives of sine-cosine potentiometer angular resolvers in controlling the repetition rate of an ultrasonic pulse-echo system. Pulse repetition rate and line display are modulated so that more pulses occur during rapid hand motion than during slow hand motions.
U.S. Pat. No. 3,918,297 discloses grey-level ultrasonic imaging which requires immersion of the subject in a tank of water or other suitable conductive fluid. Pulses reflected from the specimen are passed through an acoustic focusing lens, a converter, a signal processer, and are ultimately displayed on a cathode-ray tube or light-emitting diode display device. The converter requires the use of a two-dimensional array of acoustical transducers. The reflected acoustical waves are converted into electrical signals and ultimately into binary data which is amplitude modulated in converse or complementary relationship in respect to the acoustical pulses. In three-dimensional presentations, two cathode-ray tubes are employed.
The use of logic circuitry in processing ultrasonic signals for visual display is shown in a number of patents. See, for example, U.S. Pat. Nos. 3,830,223; 3,548,641; 3,818,898; 3,856,985 and 3,885,224. There remains, therefore, a present need for a reliable, economically practical system for taking the output of a conventional ultrasonic testing piece of apparatus and processing the signal in such fashion as to provide a grey-level visualization of the patient of specimen-generated data on a conventional storage oscilloscope.